Apparatus for measuring microvascular blood flow

Abstract

An apparatus for measuring microvascular blood flow in tissue including a monochromatic light source arranged to irradiate a section of the tissue with the monochromatic light from the light source, a photodetector arranged to collect light scattered from the irradiated section, a processor for processing the electrical output signals from the photodetector, calculating the power spectrum of photocurrents generated in the detection of laser light scattered from static tissue and Doppler broadend laser light scattered from moving blood cells, and recording the average Doppler frequency shift, and further calculating and recording the blood concentration. The apparatus further measures and records the intensity of the detected scattered light, calculates and records the blood perfusion (flux), filters movement artefact noise, and displays the blood perfusion measured parameters. By filtering movement artefact noise, the apparatus enables fast tissue blood perfusion monitoring with enhanced signal quality.

We claim:  
     
       1. An apparatus for measuring blood in tissue comprising: 
       a monochromatic laser light source;  
       means for irradiating a section of the tissue with the monochromatic light from the light source;  
       means for collecting light scattered from the irradiated section;  
       a photodetector fox detecting the collected scattered light;  
       means for processing electrical output signals from the photodetector;  
       means for calculating a power spectrum of photocurrents generated in the detection of laser light scattered from static tissue and Doppler broadened laser light scattered from moving blood cells;  
       means for calculating and recording the average Doppler frequency shift;  
       means for calculating and recording the red blood cell concentration;  
       means for measuring and recording the intensity of the detected scattered light;  
       means for calculating and recording the blood perfusion (flux);  
       means for filtering movement artefact noise by measuring changes in the photocurrent power spectrum for a low frequency band;  
       means for displaying the blood perfusion measured parameters;  
       means to judge whether a change is due to movement artefact noise by comparison of current low frequency spectral power with averaged low frequency power or by comparison of current frequency weighted low frequency spectral power (LP) with the averaged frequency (ω) weighted low frequency spectral power(LPA);  
       means to calculate a blood perfusion (flux) value in the presence of detected movement artefact noise by summing the averaged frequency (ω) weighted low frequency spectral power (LPA) with frequency weighted high frequency spectral power (HP), where:  
       
         
           Flux=Instrument Constant×( LPA+HP );  
         
       
       means to calculate a blood perfusion value in the absence of movement artefact noise by summing the current frequency weighted low frequency spectral power (LP) and the frequency weighted high frequency spectral power (HP), where:  
       
         
           Flux=Instrument Constant×( LP+HP );  
         
       
       and 
       means to calculate a blood perfusion value in the presence of movement artefact noise comprising a noise replacement filter whereby during a noise affected period the noisy signal is replaced by noise free data recorded in a period immediately prior to the noisy period.  
     
     
       2. An apparatus according to claim  1 , wherein the means for irradiating a section of tissue with monochromatic laser light is via an optic fibre and the means to collect light scattered from the tissue for photodetection is via one or more optic fibres. 
     
     
       3. An apparatus according to claim  1 , wherein the means for irradiating a section of tissue with monochromatic laser light is with a laser beam. 
     
     
       4. An apparatus according to claim  1 , wherein the signal frequency analysis, calculations of blood flow parameters and signal filtering to reduce the affects of movement artefact on the measured blood perfusion, red blood cell concentration and averaged Doppler frequency shift are carried out with the aid of fast large scale digital signal processing integrated circuits to enable real time processing and display. 
     
     
       5. An apparatus for measuring blood in tissue comprising: 
       a monochromatic laser light source;  
       means for irradiating a section of the tissue with the monochromatic light from the light source;  
       means for collecting light scattered from the irradiated section;  
       a photodetector for detecting the collected scattered light;  
       means for processing electrical output signals from the photodetector;  
       means for calculating a power spectrum of photocurrents generated in the detection of laser light scattered from static tissue and Doppler broadened laser light scattered from moving blood cells;  
       means for calculating and recording the average Doppler frequency shift;  
       means for calculating and recording the red blood cell concentration;  
       means for measuring and recording the intensity of the detected scattered light;  
       means for calculating and recording the blood perfusion (flux);  
       means for filtering movement artefact noise by measuring changes in the photocurrent power spectra for both low and high frequency bands;  
       means for displaying the blood perfusion measured paraeters;  
       means to calculate frequency (ω) weighted averaged spectral power for a low frequency band (LPA) and for a high frequency band (HPA);  
       means to judge whether changes are due to movement artefact noise by comparison of current frequency weighted low frequency spectral power (LP) with the averaged frequency weighted low frequency spectral power (LPA) and comparison of current frequency weighted high frequency spectral power (HP) with the averaged frequency weighted high frequency spectral power (HPA); and  
       means to calculate a blood perfusion (flux) value in the presence of movement artefact noise detected by said comparison by summing the averaged frequency weighted low frequency spectral power (LPA) with the current frequency weighted high frequency spectral power (HP).  
     
     
       6. An apparatus according to claim  5 , wherein the means for irradiating a section of tissue with monochromatic laser light is via an optic fibre and the means to collect light scattered from the tissue for photodetection is via one or more optic fibres. 
     
     
       7. An apparatus according to claim  5 , wherein the means for irradiating a section of tissue with monochromatic laser light is with a laser beam. 
     
     
       8. An apparatus according to claim  5 , wherein the signal frequency analysis, calculations of blood flow parameters and signal filtering to reduce the affects of movement artefact on the measured blood perfusion, red blood cell concentration and averaged Doppler frequency shift are carried out with the aid of fast large scale digital signal processing integrated circuits to enable real time processing and display. 
     
     
       9. An apparatus for measuring blood in tissue comprising: 
       a monochromatic laser light source;  
       means for irradiating a section of the tissue with the monochromatic light from the light source;  
       means for collecting light scattered from the irradiated section;  
       a photodetector for detecting the collected scattered light;  
       means for processing electrical output signals from the photodetector;  
       means for calculating the power spectrum of photocurrents generated in the detection of laser light scattered from static tissue and Doppler broadened laser light scattered from moving blood cells;  
       means for calculating and recording the average Doppler frequency shift;  
       means for calculating and recording the red blood cell concentration;  
       means for measuring and recording the intensity of the detected scattered light;  
       means for calculating and recording the blood perfusion (flux);  
       means for filtering movement artefact noise by sampling blood perfusion values at a rate comparable to the rate at which blood perfusion values are calculated;  
       means for displaying the blood perfusion measured parameters;  
       means to record the minimum perfusion value taken in a measurement period of long duration compared to the calculation period of the blood perfusion values and of short duration compared to the period for which the trend is to be recorded;  
       means to record minimum values for successive search periods; and  
       means to display the blood perfusion minimum values for long measurement periods to produce trend records substantially free of movement artefact noise.  
     
     
       10. An apparatus according to claim  9 , wherein the means for irradiating a section of tissue with monochromatic laser light is via an optic fibre and the means to collect light scattered from the tissue for photodetection is via one or more optic fibres. 
     
     
       11. An apparatus according to claim  9 , wherein the means for irradiating a section of tissue with monochromatic laser light is with a laser beam. 
     
     
       12. An apparatus according to claim  9 , wherein the signal frequency analysis, calculations of blood flow parameters and signal filtering to reduce the affects of movement artefact on the measured blood perfusion, red blood cell concentration and averaged Doppler frequency shift are carried out with the aid of fast large scale digital signal processing integrated circuits to enable real time processing and display.